Hydrocarbon recovery can be enhanced in certain heavy oil and bitumen reservoirs by drilling closely spaced vertical production and steam injection well bores into the hydrocarbon reservoir formations and injecting steam. Under this conventional thermal secondary recovery technique, the steam can cause the heavy hydrocarbons to become mobile due to the reduction of its in-situ viscosity.
Several improvements have been made to enhance recovery of heavy oils and bitumens beyond conventional thermal techniques. One such technique is U.S. Pat. No. 4,344,485 issues Aug. 17, 1982 to Butler teaches a Steam Assisted Gravity Drainage (SAGD) method where pairs of horizontal wells, one vertically above the other are connected by a vertical fracture. A steam chamber rises above the upper well and oil warmed by conduction drains along the outside wall of the chamber to the lower production well.
The benefits of SAGD over conventional secondary thermal recovery techniques include higher oil productivity relative to the number of wells employed, higher ultimate recovery of oil in place and lower steam oil ratios.
There are problems associated with typical SAGD projects more particularly:
The economics of thermally enhanced hydrocarbon recovery projects is significantly impacted by the costs associated with generating steam. The hydrocarbon fuel to fire these boilers is usually the single most significant operating cost in a thermally enhanced recovery project and SAGD project are typically shut-in when the cost of fuel and other operating costs exceed the project's revenue; and
SAGD does not typically employ the use of super saturated steam because of the high cost of producing this steam with conventional hydrocarbon fired tube boilers. This results in using 70–80% quality steam that is less efficient in transferring heat to the heavy oil reservoir; and
The produced water associated with the hydrocarbon production from these operations is typically disposed of in commercially operated disposal wells for a fee.
U.S. Pat. No. 4,007,786 issued Feb. 15, 1977 to Schlinger, attempted to address the steam generation costs associated with conventional secondary recovery thermal projects through the use of a gas turbine and electrical generator to generate steam and to produce raw fuel by partial oxidation of the produced hydrocarbons. However, this process has several shortcomings including:
It did not address the application to SAGD technology; and
It did not address a process for primary and tertiary thermal recovery projects for heavy oil and bitumen reservoirs; and
It did not address the operation of the gas turbine generator in simple or combined cycle; and
It did not address the use of superheated steam and a heat recovery and steam-generating unit (HRSG) that is employed in generating superheated steam through cogeneration.
Other inventions have been created to overcome some of these operating issues. U.S. Pat. No. 4,694,907 utilizes cogeneration and electrical down hole steam generators to attempt thermally enhanced oil recovery in deep well reservoirs. This process is focused at overcoming heat losses associated with thermal recovery operations in deep reservoirs. This process has several shortcomings:
The combination of cogeneration and down hole heaters is very expensive and its application is for deep reservoirs; and
The process does not address the use with SAGD technology.
The object of my invention is to link two distinct concepts an electrical/steam cogeneration station to generate superheated steam with SAGD and to take advantage of the economic benefits that accrue through the use of combining these technologies for primary secondary and tertiary thermal recovery in shallow heavy oil reservoirs.